The present invention is drawn to an improved ceramic foam filter for use in filtering molten metal, especially iron base alloys, and a process for preparing same. More particularly, the present invention relates to a ceramic foam filter having improved properties especially with respect to the filtration of iron and iron base alloys to the provision of rapid priming with respect thereto, and not being reactive therein.
It is known in the art to employ porous ceramic foam materials to filter molten metal especially aluminum, as described for example in U.S. Pat. Nos. 3,893,917, 3,947,363, 3,962,081, 4,024,056, 4,024,212, 4,075,303, 4,265,659, 4,342,644 and 4,343,704. The production materials for these filters comprise primarily a phosphate bonded refractory material, having certain other additions, which has been fired to a temperature of about 2000.degree. F. in order to mature the bond. While this type of refractory is suitable for use in the aluminum industry and easily withstands most aluminum alloys which are typically cast at about 1300.degree. F., it is unsuitable for many other potential applications due to low strength and poor chemical resistance and poor high temperature stability.
Naturally, it would be highly desirable to develop a material which maintains the favorable properties of the ceramic foam material heretofore known, namely, high porosity, low pressure drop, high geometric surface area and tortuous flow path, but which overcomes the foregoing difficulties of strength, chemical durability and temperature resistance. In addition, it is highly desirable to develop a material which could be relatively simply produced and used in a number of applications especially high temperature applications, such as for the filtration of ferrous metals.
U.S. Pat. No. 4,610,832 describes an improved ceramic foam filter and a process for preparing same particularly useful for high temperature applications such as ferrous or steel filtration based on the use of an aqueous slurry of a thixotropic ceramic composition including a gelled alumina hydrate binder. It has been found that for certain applications, specialized running and gating systems are needed to insured priming of this filter, although said filter does represent a significant improvement.
It is therefore a principal object of the present invention to provide an improved ceramic foam filter and a process for preparing same.
It is a further object of the present invention to provide an improved ceramic foam filter and process as aforesaid which is inexpensive and easy to perform and which results in a filter having desirable and indeed improved properties.
It is still a further object of the present invention to provide an improved filter and process as aforesaid which overcomes the shortcomings of phosphate binders and which provides a filter which is readily primed and has improved thermal properties.
Further objects and advantages of the present invention will appear hereinbelow.